1. Field of the Invention
The present invention relates generally to a method of making organo-silicon polymers and more specifically to a method of making such polymers having both mono- and tetra-functional siloxane units.
2. Description of the Prior Art
Organo-silicon polymers having both mono- and tetra-functional siloxane units are well known in the art. In the past, such polymers have generally been prepared by cohydrolysis of a hydrolyzable silane or disiloxane (which are used as the feed material for mono-functional siloxane units) and a silicate salt or an alkyl silicate (which are used as the feed material of the tetra-functional siloxane units.)
When a disiloxane is used as the feed material for the mono-functional siloxane units, the average molecular weight can be controlled, so that the organo-silicon polymer which forms can have a relatively narrow distribution of the average molecular weight.
In Japanese Kokai Patent Application No. Sho 61[1986]-195129 there is proposed such a method wherein tetraethoxysilane or another alkyl silicate is added drop-wise to a mixture of hexamethyldisiloxane or other alkyldisiloxane, concentrated hydrochloric acid, water and ethanol. The drawback of the method, however, is that when a disiloxane having C.sub.2 or higher monovalent hydrocarbon radicals is used as the feed material, the products formed therein have a tendency to gel during reaction. The gel so-formed is resistant to dissolution, even with the addition of more solvent.
In accordance with the method of the present invention, the tendency of the reaction products to gel during formation has been overcome, even when a mixture of disiloxane having C.sub.2 or higher monovalent hydrocarbon radical and alkyl silicate is used as the feed material in making the aforementioned organo-silicon polymer.